Information storage devices typically include a magnetic head for reading and/or writing data onto the storage medium, such as a disk within a rigid disk drive. An actuator mechanism is used for positioning the head at specific locations or tracks in accordance with the disk drive usage. Disk drive suspensions are provided between the actuator and the magnetic head to support the head in proper orientation relative to the disk surface.
In a rigid disk drive, head suspensions are provided which support a read/write head to “fly” over the surface of the rigid disk when it is spinning. Specifically, the head is typically located on a slider having an aerodynamic design so that the slider flies on an air bearing generated by the spinning disk. In order to establish the fly height, the head suspension is also provided with a spring force counteracting the aerodynamic lift force.
A head suspension of the type used in a rigid disk drive includes a load beam and a flexure to which the slider is mounted. The flexure is provided at the distal end of the load beam and permits pitch and roll movements of the slider to follow disk surface fluctuations. A preformed bend or radius is made in the spring region of the load beam to provide the spring force to the rigid region of the load beam for counteracting the aerodynamic lift force against a slider. The radius provides the spring force and thus a desired gram loading to the slider for a predetermined offset height, the offset height being a measurement of the distance between the mounting height of the head suspension and the slider at “fly” height. The load beam is attached to an actuator, which positions the load beam so that the magnetic head can read and/or write data to the hard disk. The data on hard disks are stored on tracks on the disk surface. As hard disks become more and more miniaturized, resulting in tracks that are positioned closer and closer together, and actuators are required to move suspension assemblies more quickly, suspension components, such as load beams, necessarily need to become smaller and have less mass.
As innovations in the disk drive industry push toward smaller drives with more closely positioned tracks and faster spinning disks, it becomes more and more advantageous to provide suspension components that are smaller and lighter so that the actuators can move the suspensions faster while requiring less power. As the disk drive suspensions become smaller and lighter and as the disk drives spin faster, the disk drive suspensions and suspension components are more and more susceptible to the effects of shock and vibration. Specifically, the suspensions and suspension components are susceptible to torsional responses and lateral responses, known as windage, from the motion of air that results from the spinning disks.
The response of the head suspension and suspension components at resonant frequencies can lead to unacceptable off-track error when attempting to read and/or write to the disk drive, unless the head suspension is designed to minimize the effects of vibration response at the resonant frequencies. Thus, it is desirable to design head suspensions to optimize performance even at resonant frequencies, to minimize the effects of the lateral bending mode and the torsional modes. More particularly, it is preferable to increase certain resonant frequencies to be higher than the vibrations experienced in the disk drive application. Additionally, it is desirable to reduce or eliminate the movement or gain of the magnetic head at the resonant frequencies of the head suspension or suspension components.
Torsional and lateral bending modes are beam modes that are dependent on cross-sectional properties along the length of the load beam. These modes also result in lateral movement of the slider at the end of the head suspension assembly. Torsional modes sometimes produce a mode shape in which the tip of the resonating head suspension assembly moves in a circular fashion. However, since the slider is maintained at an offset height by the stiffness of the applied spring force, primarily lateral motion of the rotation is seen at the slider. The lateral bending mode (often referred to as “sway”) is primarily lateral motion. It is typically desirable to control the resonant frequency of the lateral bending mode so that it is higher than the frequencies that are experienced in the disk drives within which they are to be used.
Torsional modes typically occur at lower frequencies than lateral bending modes, but typically have less of a lateral effect. Torsional modes are further subdivided depending on the number, if any, of nodes present along the length of the suspension assembly between a fixed end thereof and its free end. The slider would be supported near the free end. These various torsional mode shapes occur at different resonant frequencies. A single twist of the head suspension between a fixed end and its free end is referred to as first torsion mode. The off-track motion at the first torsion resonant frequency is the first torsional gain. Second torsional mode means a torsional mode shape having a single node along the length of the suspension between its fixed end and its free end. The position of the node divides the head suspension into first and second twisting motions on either side of the node point. Second torsional resonant frequencies occur at higher frequencies than the first torsional mode. Higher order torsional modes, i.e., third torsional mode having two node points, etc., typically occur at frequencies higher than those experienced within a disk drive environment.
To provide a high lateral bending frequency, the head suspension needs to be stiff in both the lateral direction and torsionally along the entire length of the head suspension. If a head suspension is designed with only one of these conditions in mind, the head suspension may have a low resonant frequency of torsional or lateral bending with a high degree of off-track motion or gain. A head suspension having a high lateral stiffness but a low torsional stiffness will not move strictly laterally due to the high lateral stiffness, but may twist at a lower resonant frequency. If the head suspension has high torsional stiffness and low lateral stiffness, the head suspension may deflect primarily laterally at a lower resonant frequency.
A number of design approaches have been used to improve the lateral and torsional vibration response of load beams, especially with respect to load beams that incorporate thinner materials. One approach is to align the notch responses of the different vibration modes to reduce the gain or movement of the load beam at the resonant frequencies. The notch response for a particular vibration mode is the minimum gain at the resonant frequency of the mode. It is desirable to align the notch response for both the lateral mode and torsional modes to improve the response of the load beam at the resonant frequencies.
One known approach used to align notches is to form a so-called “sag” bend across the rigid region of the load beam. By adding the sag bend to a load beam, it is possible to properly align the center of rotation of the suspension assembly with respect to the load point dimple and align first and second torsional notch responses. However, as load beam materials become thinner (load beams having a thickness of less than 40 μm are now common) and as the mass of load beams are reduced by removing material along a major surface of the load beam, it becomes increasingly difficult to incorporate a sag bend across the major surface.
Another known approach is to design a load beam with a top profile to reduce the effects of vibration. Alternatively, or in addition, stiffening plates can be attached to the rigid region of a load beam to improve vibration response. Approaches of these type are described in U.S. Pat. No. 5,850,319, which is hereby incorporated by reference. Still other approaches have included adding rails along the edges of the rigid region of the load beam to stiffen the load beam. A number of approaches have used rails along the edges of rigid regions having a top profile that is defined by one or more linear segments. In other applications, side rails more than one segment have been incorporated onto load beams with a transition region between linear segments. It has been recognized in at least some of these load beams that the transition point becomes a weak point with respect to withstanding respect to resonant response relative to the remainder of the rails.
What is needed are disk suspension assemblies and assembly components that can be made of thinner materials and yet have improved vibration response with respect to lateral and torsional excitation. Such assemblies and assembly components should be efficient to manufacture.